The present invention relates to an image processing apparatus with an automatic window processing function which is well fitted to adapt to X-ray digital fluorography, said window processing serving to improve the quality of an image displayed at a monitor by changing the contrast of the image.
A typical application of an image processing apparatus with a window processing function is, e.g., an X-ray diagnostic apparatus used in X-ray digital fluorography. Such an apparatus may have a configuration as shown in FIG. 1. In this figure, numeral 1 denotes an X-ray tube. Tube 1 radiates an X-ray to an inspection body 3 upon receiving a high voltage from a high voltage generation apparatus 2. Numeral 4 denotes an image intensifier. Intensifier 4 responds to an X-ray passing through inspection body 3 and converts an image of the passing X-ray into an optical image. The optical image from intensifier 4 is projected onto an image pickup tube via an optical system 5 which contains an iris stop. The image pickup tube is installed in a TV (television) camera head 6. The projected image is obtained as an image signal E7 through a conventional camera control unit 7.
Image signal E7 is supplied to an image processor 8. Processor 8 includes an input selector 9 which receives image signal E7. Selector 9 selects the signal E7 as a selected signal E9. Selected signal E9 is supplied via a switch either directly to an A/D converter 11, or, via a logarithmic function converter (so called "log amplifier") 10 to A/D converter 11 according to the selection of the switch. Signal E9 is converted by A/D converter 11 into a digital image signal D11. Signal D11 is arithmetically processed in a prescribed manner in an arithmetic and logic unit (ALU) 12. An arithmetically processed signal D134 obtained from ALU 12 is stored in a first frame memory 13. The stored contents in first frame memory 13 represents an X-ray image of inspection body 3 to which no X-ray contrast medium is injected. Similarly, another arithmetically processed signal D134 from ALU 12 is stored in a second frame memory 14. Second frame memory 14 may have the same configuration as first frame memory 13. The stored contents in second frame memory 14 represents an X-ray image of inspection body 3 to which an X-ray contrast medium is injected.
One of the above two arithmetically processed signals (D134) stored in frame memories 13 and 14 is subtracted in ALU 12 from the other, so that a subtracted image signal D12 is generated. Subtracted image signal D12 is supplied to an image emphasis circuit (window circuit) 15. In circuit 15, the contrast of an image of signal D12 to be displayed is changed or emphasized. A contrast-emphasized image signal D15 corresponding to signal D12 is obtained from image emphasis circuit 15. Signal D15 (digital in form) is converted to an analog image signal E16 via a D/A converter 16. Signal E16 is supplied to a monitor 17 located at the outside of processor 8. In monitor 17, an image of signal E16 is displayed. At the same time, signal E16 is supplied to a video disc recorder 18, and the image information of signal E16 is recorded on a video disc. Further, signal E16 is transferred to a multiformat camera 19 in which the transferred signal is photographed on a film. A reproduced image signal E18 from recorder 18 is supplied to input selector 9. When selector 9 selects signal E18 in place of signal E7, processor 8 performs the above-mentioned signal processing for signal E18.
In FIG. 1, numeral 20 denotes an X-ray interface for interfacing the high voltage generation apparatus 2 with the image processor 8. Numeral 21 denotes an operation panel (for processor 8, etc.) & system controller which controls apparatus 2 via interface 20 or which manipulates the respective elements of processor 8.
Incidentally, the configuration of FIG. 1 may be modified or replaced by one as disclosed in U.S. Pat. No. 4,204,225 (Mistretta) issued on May 20, 1980 or U.S. Pat. No. 4,204,226 (Mistretta et al.) issued on May 20, 1980. All disclosures of these U.S. patents are incorporated in the present application.
According to an X-ray apparatus as mentioned above, information D21 of a gradation range (hereinafter referred to as "WIDTH") and gradation level (hereinafter referred to as "LEVEL") for window processing is supplied from operation panel/system controller 21 to image emphasis circuit 15. Then, window processing is performed in circuit 15 so as to improve the quality of a displayed image, by changing the contrast of the image according to the values of LEVEL and WIDTH. An example of a window table indicating the relation among input D12, output D15, LEVEL and WIDTH in the window processing is shown in FIG. 2. In FIG. 2, window input D12 is represented by 10 bits data (0 to 1023 in decimals) and window output D15 is represented by 8 bits data (0 to 255 in decimals). In order to obtain 8-bit image data (D15) without substantially reducing the quantity of 10-bit input information (D12), the window table as shown in FIG. 2 is provided.
Using an apparatus as shown in FIG. 1, it is difficult to quickly determine an optimum value of each of LEVEL and WIDTH by viewing the image displayed at monitor 17. In other words, it is not easy to optionally determine, by viewing the monitor, the desired values of LEVEL and WIDTH by experimentally changing the values of LEVEL and WIDTH. Thus, in using the above-mentioned apparatus, in which the values of LEVEL and WIDTH are individually determined by various operators, much skill and time is required for the window processing. In addition, the contrast of an image obtained according to the above described window processing is not always optimal.